U.S. patent application number 12/158031 was filed with the patent office on 2009-08-13 for polyaxial bone anchor with headless pedicle screw.
Invention is credited to Felix Aschmann.
Application Number | 20090204155 12/158031 |
Document ID | / |
Family ID | 37909698 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090204155 |
Kind Code |
A1 |
Aschmann; Felix |
August 13, 2009 |
POLYAXIAL BONE ANCHOR WITH HEADLESS PEDICLE SCREW
Abstract
A polyaxial bone anchor has a headless anchor member (e.g., a
screw, hook, or other structure for attaching to bone) that allows
the size of the bone anchor to be small. A locking element securely
snap-fits over the headless anchor member such that inadvertent
separation from the anchor member is unlikely. When the anchor
member is attached to the locking element and the locking element
is seated within the anchor head of the bone anchor, the headless
anchoring member can polyaxially rotate about a central axis of the
bone anchor before being locked in place.
Inventors: |
Aschmann; Felix; (Basel,
CH) |
Correspondence
Address: |
STROOCK & STROOCK & LAVAN, LLP
180 MAIDEN LANE
NEW YORK
NY
10038
US
|
Family ID: |
37909698 |
Appl. No.: |
12/158031 |
Filed: |
December 15, 2006 |
PCT Filed: |
December 15, 2006 |
PCT NO: |
PCT/US2006/047986 |
371 Date: |
October 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60752016 |
Dec 19, 2005 |
|
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|
Current U.S.
Class: |
606/264 ;
606/301; 606/305 |
Current CPC
Class: |
A61B 17/7032 20130101;
A61B 17/7037 20130101 |
Class at
Publication: |
606/264 ;
606/301; 606/305 |
International
Class: |
A61B 17/70 20060101
A61B017/70; A61B 17/86 20060101 A61B017/86 |
Claims
1-17. (canceled)
18. A polyaxial bone anchor for attaching a rod to a bone
comprising: an anchor head comprising a longitudinal bore having a
top opening and a bottom opening, a generally U-shaped channel
transverse to the longitudinal bore for receiving the rod, and a
central axis extending through the bore; a headless anchor member
having a top, a bottom, and a shank, the shank having a
non-threaded portion adjacent to the top of the anchor member, the
non-threaded portion having a substantially constant diameter, and
a bone engaging portion adjacent to the bottom of the anchor
member, the bone engaging portion of the anchor member extending
through the bottom opening of the anchor head for attaching to
bone; a locking member configured to be retained within the anchor
head and to receive at least a portion of the non-threaded portion
of the shank, the non-threaded portion of the shank includes an
exterior groove adjacent to the top of the anchor member and the
locking member has an interior ridge positionable in the groove of
the non-threaded portion of the shank when the non-threaded portion
of the shank is fully received within the locking member, the
locking member operative to angulate about the central axis in all
directions; and a fastener removably mountable to the anchor head
to close the top opening of the bore and to lock both the position
of the rod in the U-shaped channel and the angulation of the
locking member.
19. The polyaxial bone anchor of claim 18, wherein the bone
engaging portion of the shank is threaded.
20. The polyaxial bone anchor of claim 18, wherein the bone
engaging portion of the shank is a hook.
21. The polyaxial bone anchor of claim 20, wherein the hook is
integrally formed with the non-threaded portion of the shank.
22. The polyaxial bone anchor of claim 18, wherein the locking
member contacts the anchor head and rotates within the anchor head
prior to the fastener locking the positions of the rod and anchor
member.
23. The polyaxial bone anchor of claim 18, wherein the locking
member comprises a collet having a plurality of resilient fingers
for compressing against the non-threaded portion of the shank, at
least two of the fingers having the interior ridge.
24. The polyaxial bone anchor of claim 18, wherein the locking
member has at least a part spherical exterior shape.
25. The polyaxial bone anchor of claim 18, wherein the locking
member has an interior area sized and shaped to substantially match
the size and shape of the non-threaded portion of the shank.
26. The polyaxial bone anchor of claim 18, further comprising a
hollow sleeve having a generally U-shaped channel for receiving the
rod, the sleeve retained within the anchor head.
27. The polyaxial bone anchor of claim 26, wherein the sleeve has a
bottom surface that engages the locking member.
28. The polyaxial bone anchor of claim 18, wherein when the spinal
rod is locked in position in the U-shaped channel, the spinal rod
contacts the top of the locking member.
29. The polyaxial bone anchor of claim 18, wherein the anchor head
has an interior surface around the bottom opening that contacts a
portion of the exterior surface of the locking member.
30. The polyaxial bone anchor of claim 18, wherein the anchor head
has a tapered interior surface around the bottom opening that
contacts and substantially matches the contour of a portion of the
exterior surface of the locking member.
31. The polyaxial bone anchor of claim 18, wherein the fastener is
a locking cap comprising a locking ring and set screw.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to bone fixation devices and related
methods of fixation. More particularly, this invention relates to
polyaxial bone anchors having headless screws and hooks, and more
specifically, polyaxial pedicle screws and hooks, for use in, for
example, the fixation of the spine.
BACKGROUND OF THE INVENTION
[0002] Polyaxial bone anchors and methods of use in treating spinal
disorders are known. Typical methods involve anchoring at least two
screws or hooks into the vertebrae, and fixing the screws or hooks
along a spinal rod to position or immobilize the vertebrae with
respect to one another. The screws or hooks (referred to
hereinafter as anchor members) commonly have anchor heads with
U-shaped channels in which the spinal rod is inserted and
subsequently clamped by a fastener, such as, for example, a
threaded nut, set screw, or locking cap. These methods commonly
involve multiple anchor members and multiple spinal rods. The
spinal rods may be shaped to maintain the vertebrae in a desired
orientation so as to correct the spinal disorder at hand (e.g., to
straighten a spine having abnormal curvature). Additionally or
alternatively, anchor members may be spaced along the rods(s) to
compress or distract adjacent vertebrae or bilaterally move
vertebrae.
[0003] Surgeons may encounter difficulty with spinal fixation and
stabilization methods because of difficulty aligning the spinal
rod(s) with the U-shaped channels in the anchor heads. For example,
anchor heads are often out of alignment with one another because of
the curvature of the spine or the size and shape of each vertebrae.
To facilitate easier insertion of the spinal rods into the U-shaped
channels, and to provide additional flexibility in the positioning
of the spinal rods and the anchor members, bone anchors have been
developed where the anchor member and anchor head can initially
pivot or rotate with respect to each other. These bone anchors are
sometimes referred to as polyaxial bone anchors and the pivot or
rotation of the anchor member is referred to as angulation.
[0004] A disadvantage of many polyaxial bone anchors is their large
size, particularly that of the anchor head, which tends to be large
in order to accommodate the typically bulbous or ball-shaped end of
the anchor member. These anchor member ends, often referred to as
the "head" of the anchor member, provide known anchor members with
their polyaxial capability. However, such large polyaxial bone
anchors may have limited application in view of the confined space
around the human spine. It may therefore be advantageous to provide
smaller polyaxial bone anchors.
SUMMARY OF THE INVENTION
[0005] The invention is directed to polyaxial bone anchors and
methods of use for attaching a rod, such as a support or spinal
rod, to a bone, such as a vertebra. The bone anchor may include a
hollow, generally cylindrical housing, body, or head (referred to
hereinafter as an anchor head), a headless anchor member (such as,
for example, a pedicle screw, hook, or other structure for
attaching to bone), an internal locking element, an optional hollow
generally cylindrical internal sleeve, and an optional fastener.
The fastener may be a threaded outer ring with set screw, but
alternatively, may be of other types or arrangements, such as, for
example, a locking cap with set screw, a threaded nut, or a locking
sleeve mounted on or over the top portion of the anchor head. The
anchor head and optional internal sleeve may have a U-shaped
channel for receiving a support/spinal rod (referred to hereinafter
as a spinal rod or rod). The locking element preferably is sized
and shaped to snap-fit onto the headless anchor member. The
fastener may close the top opening of the U-shaped channel after a
rod has been placed therein and, in combination with the locking
element, lock or clamp the respective positions of the anchor
member and spinal rod with respect to each other and the anchor
head.
[0006] The headless anchor member has a shank with a non-threaded
portion. In the case of a pedicle screw, the shank also has a
threaded portion for insertion into bone. In the case of a pedicle
hook, the shank is integrally or discretely connected to a hook
structure that attaches to bone. Similarly, for other types of
anchor members, the shank with the non-threaded portion may be
integrally or discretely connected to other structures for
attaching to bone.
[0007] The non-threaded shank portion preferably has a circular
cross section, but may be of other cross-sectional shapes, such as,
for example, polygonal. The non-threaded portion preferably has a
constant diameter or width throughout its length and preferably has
an external groove around its circumference or perimeter (the
groove is not part of any thread). The non-threaded portion is not
integrally connected to an enlarged end (e.g., a spherically or
partially spherically shaped end). Such an enlarged end is often
referred to as the "head" of the anchor member. Anchor members of
the invention may thus be referred to as "headless."
[0008] The locking element, internal sleeve, and anchor head have
features that allow the locking element to rotate and/or pivot
within the anchor head. This in turn allows the anchor member to
angulate in all directions around and away from a central axis
running through a bottom opening in the anchor head. The anchor
member may then be locked at a desired angle and direction with
respect to the anchor head.
[0009] The locking element, which may be a collet or collet-styled
bushing, has a spherical or at least a partially spherical exterior
shape. This spherical exterior shape allows the locking element to
rotate and/or pivot within the anchor head, which in turn allows
the anchor member to angulate in all directions about the central
axis. The interior area of the locking element is sized and shaped
slightly smaller than the size and shape of the non-threaded shank
portion of the anchor member in order that the locking element be
snap-fitted over the non-threaded shank portion. The locking
element has a plurality of resilient fingers that radially expand
to initially receive the non-threaded shank portion. Preferably,
each finger has an interior ridge that sits in the external groove
of the non-threaded shank portion when that portion is fully
received in the locking element. This ridge-groove feature lessens
the likelihood of the anchor member inadvertently separating from
the locking element. The locking element preferably is configured
to receive at least the uppermost portion of the non-threaded shank
portion, with the remaining portion of the anchor member extending
through the bottom opening of the anchor head.
[0010] The generally cylindrical internal sleeve has a bottom
surface that preferably tapers or curves inward and upward such
that when positioned in the anchor head it contacts the top
exterior surface of the locking element fingers. This facilitates
locking of the anchor member to the locking element, while allowing
pivoting or rotation of the locking element prior to locking. In
particular, when the anchor member is ready to be locked (i.e., the
anchor member is positioned as desired), the fastener is tightened,
causing the bottom surface of the internal sleeve to press down on
the outside of the locking element fingers, which compress around
the non-threaded shank portion to lock the position of the anchor
member.
[0011] The anchor head has a lower portion with an interior surface
around the bottom opening that is preferably tapered or spherically
or partially spherically shaped to substantially match and contact
a portion of the exterior surface of the locking element. This also
facilitates pivoting and/or rotation of the locking element within
the anchor head prior to locking.
[0012] By not requiring the typically large heads of known anchor
members in order to provide polyaxial capability, a polyaxial bone
anchor, and in particular its anchor head, can have a small size.
This small size advantageously improves the versatility of the bone
anchor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The detailed description will be better understood in
conjunction with the accompanying drawings, in which like reference
characters refer to like parts throughout, and in which:
[0014] FIGS. 1-3 are perspective, partial cutaway perspective, and
exploded perspective views, respectively, of a known polyaxial bone
anchor;
[0015] FIGS. 4 and 5 are perspective and partial cutaway
perspective views of a polyaxial bone anchor with a headless
pedicle screw according to the invention;
[0016] FIG. 6 is an exploded perspective view of the polyaxial bone
anchor of FIGS. 4 and 5; and
[0017] FIG. 7 is an enlarged partial cutaway view of the anchor
head, internal locking element, and headless anchor member of the
polyaxial bone anchor of FIGS. 4-6.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The invention can be used to treat various spinal disorders
including, for example, degenerative and other instabilities due to
decompression, tumors, infections, and fractures.
[0019] Note that while the polyaxial bone anchor is described and
illustrated herein with reference to certain preferred or exemplary
embodiments, the invention should not be limited to those preferred
or exemplary embodiments. Furthermore, the features described and
illustrated herein can be used singularly or in combination with
other features and embodiments.
[0020] FIGS. 1-3 show a known polyaxial bone anchor. Polyaxial bone
anchor 100 includes a fastener 102, an anchor head 104, and an
anchor member 106. A spinal rod 108 may be clamped or locked in
bone anchor 100, while anchor member 106, which may be a pedicle
screw, hook, or other similar structure (and is referred to
hereinafter as pedicle screw 106) may be inserted into or attached
to bone. Bone anchor 100 may also include a locking element 110, an
internal sleeve 112, and a saddle 114. Fastener 102 may include a
set screw 116 and a threaded outer body 118.
[0021] Anchor head 104 is cylindrically hollow having a
longitudinal bore 122 along longitudinal axis 124. Longitudinal
bore 122 is bounded by a top opening 128 and a bottom opening 130
in anchor head 104. Anchor head 104 also has a generally U-shaped
opening 126 transverse to longitudinal bore 122 for receiving
spinal rod 108 or other similar part.
[0022] Pedicle screw 106 has a shank 132, neck 134, and head 136.
Neck 134 may have a smaller diameter or width than shank 132, while
head 136 has a gradually increasing diameter or width along the
length of the screw until its maximum diameter or width is reached
at or near the top of the screw. Although head 136 is
frusta-spherical, many known embodiments of pedicle screws have
fully or substantially spherical or bulbous heads, in which case
the diameter or width along the screw length decreases from its
maximum until the top of the screw is reached. Head 136 of pedicle
screw 106 may also be partially spherically shaped.
[0023] Locking element 110 may be a collet or collet-styled bushing
having a large resilient bottom opening 137. The diameter of the
bottom opening is slightly less than the diameter of head 136.
Locking element 110 also has a plurality of resilient fingers 138.
The resiliency of opening 137 and fingers 138 is provided in large
part by slots 140. Opening 137 and fingers 138 both expand to allow
the enlarged head 136 of pedicle screw 106 to be inserted within
locking element 110. As shown, slots 140 may alternately extend
from each end of locking element 110. While the arrangement,
shapes, and dimensions of the slots and fingers may be different in
other known locking elements, they generally perform substantially
they same function: to initially expand, hold, and then lock in
place the pedicle screw. Locking element 110 may also have a lip
142 that snaps into a groove 144 on an interior surface of the
lower portion of anchor head 104. Groove 144, which is not a part
of a thread, holds locking element 110 in place within anchor head
104. The pedicle screw alone may be implanted in bone first, and
the anchor head/locking element assembly snap-fitted over the screw
head thereafter. With locking element lip 142 snapped into anchor
head groove 144, and screw head 136 snapped into locking element
110, the neck and shank of pedicle screw 106 extend out of bottom
opening 130 of anchor head 104. Prior to being locked or clamped in
place, head 136 provides pedicle screw 106 with the capability of
polyaxially (or angularly) rotating or pivoting by an angle .theta.
around central axis 124. Angle .theta. in known polyaxial bone
anchors is typically about 10-15.degree. (i.e., the angular
rotation of pedicle screw 106 forms a cone of typically about
20-30.degree.), although angle .theta. may also extend to
25-30.degree. resulting in an angular rotation that forms a cone of
about 60.degree. or less.
[0024] Optional internal sleeve 112 may be inserted downward
through top opening 128 into anchor head 104. Sleeve 112 is hollow
and generally cylindrical and may have a generally U-shaped channel
143 for receiving a rod. Sleeve 112 has a bottom opening 145 that
fits over locking element fingers 138. If pedicle screw 106
includes sleeve 112, the outside surface of the locking element, or
at least a portion thereof, may interact with the interior surface
146 of sleeve 112, instead of interacting with the interior of
anchor head 104. The portion of interior sleeve surface 146
positioned over fingers 138 may be tapered to facilitate locking.
The outside or exterior surface of the locking element may have a
tapered surface to correspond to the interior surface of the
sleeve. Bottom edge 148 of sleeve 112 may be positioned above or
rest on lip 142 of locking element 110. Sleeve 112 may further have
a pair of tabs 150 on each side of its U-shaped channel that sit at
the bottom corners of U-shaped opening 126 of anchor head 104 to
align the U-shaped channel with the U-shaped opening.
[0025] Optional set screw 116 may have external threads 156 that
mate with internal threads 158 of outer body 118. Set screw 116 may
also have a flared bottom 160 to prevent it from being screwed out
of outer body 118. Set screw 116 may further be preloaded into
outer body 118 before fastener 102 is attached to anchor head
104.
[0026] Optional saddle 114 has an upper portion 154 that fits into
set screw 116. The set screw may rotate relative to and over saddle
114. Saddle 114 facilitates clamping or locking of rod 108. A
recess 152 in saddle 114 has a radius of curvature that may be the
same as, or slightly smaller than, spinal rod 108. As set screw 116
is driven downward, it pushes and then clamps saddle 114 over and
onto spinal rod 108.
[0027] With a spinal rod in the U-shaped channel and saddle 114
either positioned in anchor head 104 on top of the spinal rod or
inserted into set screw 116, fastener 102 may be attached to anchor
head 104 by first threading outer body threads 161 into anchor head
threads 163a,b on respective interior surfaces of upper arms 120a,b
of the anchor head. This closes top opening 128. At this stage,
bone anchor 100 is unlocked, meaning that pedicle screw 106 is free
to angulate and rod 108 is free to slide in and out of U-shaped
opening 126 (although it can no longer be removed through top
opening 128). Upon satisfactory positioning of the pedicle screw
and rod, set screw 116 may be driven downward to lock the screw and
rod in place. As set screw 116 is driven downward, saddle 114
contacts rod 108, pushing it downward. Then, depending on the
design of the bone anchor, rod 108 may then contact sleeve 112,
pushing it down against locking element 110, or saddle 114 and/or
rod 108 may push down on locking element 110. In any case, contact
with locking element 110 causes resilient fingers 138 to compress
around and ultimately crush-lock head 136 of pedicle screw 106,
clamping both the pedicle screw and spinal rod in place.
[0028] Note that while the parts shown in FIGS. 1-3 are merely
representative of known polyaxial bone anchors--the exact
arrangement, shapes, and connection of such parts may vary--the
assemblage of such known polyaxial bone anchor parts is likely to
result in a large, bulky bone anchor. For example, representative
exemplary dimensions of a known bone anchor 100 may include an
anchor head height of about 12 mm, a width of about 10 mm, and a
depth of about 8.5 mm. Pedicle screw 106 may have a shank diameter
of about 4 mm, a neck diameter of about 2.75 mm, and a maximum head
diameter of about 5.4 mm. Alternatively, other known bone anchors
may be of other similarly large dimensions.
[0029] FIGS. 4-7 show a polyaxial bone anchor with a headless
pedicle screw. Polyaxial bone anchor 400 preferably includes
optional fastener 402, anchor head 404, headless pedicle screw 406,
internal locking element 410, optional internal sleeve 412, and
optional saddle 414. Anchor head 404, locking element 410, and
internal sleeve 412 are designed such that headless pedicle screw
406 can polyaxially rotate with respect to anchor head 404. One or
more polyaxial bone anchors 400 may be attached to, for example,
the vertebrae via respective anchor members 406, and a spinal rod
108 or other similar part can be inserted into the U-shaped
openings 426 of respective anchor heads 404. The spinal rod may
thereafter be locked with respect to anchor heads 404. A system of
bone anchors and rods can be used to correctly align the spine or
treat other spinal disorders.
[0030] FIG. 6 shows the various parts of bone anchor 400, which
includes outer ring 418 and set screw 416 of optional fastener 402,
optional saddle 414, spinal rod 108, optional internal sleeve 412,
locking element 410, headless pedicle screw 406, and anchor head
404. Anchor head 404 is preferably cylindrically hollow having a
longitudinal bore 422 along longitudinal axis 424. Longitudinal
bore 422 is bounded by a top opening 428 and a bottom opening 430
in anchor head 404. Anchor head 404 also has a generally U-shaped
opening 426 transverse to longitudinal bore 422 for receiving
spinal rod 108 or other similar part.
[0031] Headless pedicle screw 406 has a shank 432 with a threaded
portion 433 and a non-threaded portion 436. The threaded portion is
for insertion into bone. The non-threaded portion preferably has a
circular cross section, but alternatively may have other
cross-sectional shapes, such as, for example, polygonal. The
non-threaded portion also has a preferably constant diameter
throughout its length and preferably has an external groove 462
around its circumference. Non-threaded portion 436 is not
integrally connected to a "head," i.e., a top portion that expands
outward (e.g., a spherically or partially spherically shaped
portion) or any other structure that is otherwise enlarged (e.g., a
circumferential bead or lip). The top 464 of pedicle screw 406
preferably has a recess or slot (not shown) keyed to receive a hex
wrench, torque wrench, or other known driver or tool to implant the
pedicle screw by rotating into, for example, a bone such as a
vertebra.
[0032] Polyaxial bone anchor 400 may first be assembled by
snap-fitting locking element 410 over non-threaded portion 436 of
headless pedicle screw 406 and inserting that assembly screw-shank
first through top opening 428 of anchor head 404. Locking element
410 is configured to receive at least the uppermost portion of
non-threaded portion 436, with the remaining portion of pedicle
screw 406 (i.e., threaded portion 433 and lowermost portion 436b)
extending through bottom opening 430 of anchor head 404.
Alternatively, headless pedicle screw 406 may be inserted into bone
and thereafter locking element 410 may be assembled to non-threaded
portion 436 of the pedicle screw.
[0033] Locking element 410 may be described as a collet or
collet-styled bushing (referred to hereinafter as collet 410) made
of a resilient material that can be compressed around the
non-threaded portion of pedicle screw 406 to retain pedicle screw
406 securely in place. Preferably, the material of the collet is
softer than the material of internal sleeve 412 and pedicle screw
406. Interior area 466 of collet 410 is sized and shaped to be
preferably slightly smaller than the size and shape of non-threaded
shank portion 436, such that the collet has to be pressed over the
non-threaded portion in a friction fit. Collet 410 has a plurality
of resilient fingers 438 preferably tapered inward that can
radially expand or deflect outward to receive non-threaded portion
436 within interior area 466. Fingers 438 are created by slots 440,
which extend from the top end of collet 410 (the top being defined
as facing anchor head top opening 428). Slots 440 may have a radius
or circular shaped portion (not shown) to provide stress relief
and/or greater resiliency to fingers 438. The arrangement, shapes,
and dimensions of the fingers and slots may be alternatively
different than shown.
[0034] Preferably each, and at least two, of fingers 438 have an
interior ridge 468 that snaps into external groove 462 of the
non-threaded shank portion when that portion is fully received in
the collet. This ridge-groove feature lessens the likelihood of
headless pedicle screw 406 inadvertently separating from collet 410
during angulation or other manipulation.
[0035] Collet 410 preferably has a spherical or at least a
part-spherical exterior shape. This exterior shape advantageously
allows collet 410 to rotate or swivel about central axis 424 within
anchor head 404 prior to the locking of the pedicle screw. The
exterior surface of collet 410 contacts and is movable and
preferably pivotable with respect to lower-portion inner surface
470 of anchor head 404. This in turn allows pedicle screw 406 to
angulate in all directions with respect to anchor head 404. The
geometry of the collet, being generally spherically or partially
spherically shaped, provides in large part the polyaxial
capability, thus allowing the pedicle screw to go "headless." Note
that collet 410 has no projections, grooves, lips, or other
features that fix collet 410 to the anchor head.
[0036] Further facilitating the angulation capability of pedicle
screw 406 is the preferably tapered inner surface 470 of anchor
head 404. Inner surface 470 preferably has two radii of curvature,
as shown in FIG. 7. The first radius of curvature at inner surface
472 substantially matches that of the spherical exterior surface of
collet 410 and allows collet 410 to contact, rotate, and pivot in
anchor head 404. The second radius of curvature or conical taper at
inner surface 474 is preferably greater than that of the collet's
spherical exterior surface to allow the bottom edge 448 of internal
sleeve 412 to fit between the collet and inner surface.
[0037] Internal sleeve 412 may be inserted downward into anchor
head 404 through top opening 428, and may be preassembled in anchor
head 404. Internal sleeve 412 is hollow and generally cylindrical
having a longitudinal bore 477 there through. Internal sleeve 412
preferably has a generally U-shaped channel 475 for receiving a
rod. U-shaped channel 475 is transverse to the longitudinal bore.
Internal sleeve 412 may also have one or more tabs 450 on each
outer side of U-shaped channel 475. The tabs align the sleeve in
anchor head 404 and are positioned respectively on each side of
U-shaped opening 126. When sleeve 412 is positioned in the anchor
head, the lower portion of the sleeve fits between anchor head
inner surface 474 and the exterior surface of collet fingers 438.
Sleeve 412 has an inner bottom surface 446 that preferably tapers
or curves inward and upward to preferably match the contour of the
exterior surface of collet fingers 438. This facilitates pivoting
or rotation of collet 410 prior to locking. To lock the angulation
of the bone anchor (e.g., when the pedicle screw and spinal rod are
positioned as desired), the sleeve is moved toward bottom opening
430 of the anchor head. As the sleeve moves downward, the sleeve's
tapered inner bottom surface 446 presses on the exterior surface of
fingers 438 to compress them around the non-threaded shank portion,
locking the position of the pedicle screw. This compression not
only acts to lock pedicle screw 406 in anchor head 404, but also
serves to keep collet 410 attached to pedicle screw 406.
[0038] With fastener 402 removed from the assembly of anchor head
404, internal sleeve 412, collet 410, and headless pedicle screw
406, the pedicle screw may be attached to a bone. A tool, such as a
hex wrench, torque wrench, or other known driver, may be inserted
through the aforementioned assembly into the recess or slot at the
top of pedicle screw 406. The screw may then be rotated, implanting
it in, for example, a bone such as a vertebra.
[0039] Anchor head 404 may now be aligned to receive a rod 108. In
one embodiment of the invention, rod 108 is preferably snapped into
internal sleeve 412. The distance between upright arms 476a,b of
sleeve 412 across U-shaped channel 475 is preferably slightly less
than the diameter of rod 108. In this manner, the sleeve may
provisionally retain the spinal rod but still permit the rod to
slide in or be removed from the U-shaped channel. Alternatively,
the distance between upright arms 476a,b may be slightly greater
than the diameter of rod 108 and the rod may simply be placed in
U-shaped channel 475.
[0040] With a spinal rod in the U-shaped channel, optional saddle
414 may be placed in anchor head 404 such that
oppositely-positioned saddle legs 478a,b straddle rod 108 and
oppositely-positioned openings 480a,b on the upper portion of
saddle 414 face respective internal threads 482a,b on anchor head
404.
[0041] Set screw 416 has external threads 484 that mate with
internal threads 486 of outer ring 418. Preferably, set screw 416
is preloaded into outer ring 418 before fastener 402 is attached to
anchor head 104, and preferably set screw 416 cannot be screwed out
of outer ring 418 (set screw 416 may have, for example, a flared
bottom (not shown) to prevent it from being screwed out). Set screw
416 preferably has a star socket 488 or other type of socket or
recess keyed to a known driver or tool. Preferably, the same tool
or driving mechanism used to attach outer ring 418 to anchor head
404 can be used in a continuous action to further rotate set screw
416.
[0042] Fastener 402 (i.e., set screw 416 preferably preloaded into
outer ring 418) may now be placed on anchor head 404, closing the
U-shaped channel. Outer ring 418 attaches to anchor head 404 by
engaging internal threads 482a,b on anchor head 404 with its
external threads 490 through respective openings 480a,b in saddle
414. As outer ring 418 is screwed down into anchor head 404, it
pushes down on saddle 414, which in turn causes saddle 414 to push
down on rod 108 and the bottoms of saddle legs 478a,b to push down
on respective upright arms 476a,b of sleeve 412. Inner bottom
surface 446 and bottom edge 448 of sleeve 412 then press down on
collet fingers 438 until, in one embodiment, sleeve 412 can no
longer move downward in the space between anchor head inner surface
474 and collet fingers 438, or, in another embodiment, tabs 450
contact the bottom edge of U-shaped opening 426 on anchor head 404.
Pedicle screw 406 is now provisionally locked in place, while rod
108 can still slide in and out of U-shaped channel 475. Note that
placement of rod 108 in the U-shaped channel is not required to
provisionally lock pedicle screw 406 in place. That is, rod 108 may
be inserted in U-shaped channel 475 after pedicle screw 406 has
been provisionally locked in place.
[0043] At this point, outer ring 418 can no longer be rotated
downward and rod 108 can still be positioned (e.g., moved) relative
to anchor head 404 and pedicle screw 406. Upon satisfactory
positioning of rod 108, set screw 416 can be driven downward to
lock the rod in place in the anchor head. As set screw 416 is
driven downward, it contacts and presses down on rod 108. Rod 108
in turn moves down the bore of the anchor head until it contacts
and presses down on pedicle screw top 464. Further downward
rotation of set screw 122 applies pressure to the spinal rod,
clamping the rod in a final position in anchor head 404 such that
the rod cannot slide and/or be removed from the anchor head. The
downward pressure applied by the rod on pedicle screw top 464 may
further compression lock pedicle screw 406 by tightly wedging
collet 410 between anchor head inner surface 472 and the
non-threaded shank portion.
[0044] Alternatively, pedicle screw 406 can be locked with respect
to the anchor head by placing rod 108 in the anchor head and
pushing down on rod 108 so that rod 108 pushes down on sleeve 412.
This in turn compresses collet 410 and locks (i.e., prevents) the
angulation of the pedicle screw in the anchor head. With this
method, the fastener and saddle do not have to be engaged or
connected to the anchor head to lock the position of the pedicle
screw relative to the anchor head--yet, a user can move or remove
rod 108. Alternatively, the fastener and saddle can be applied to
the anchor head while the force to lock the angulation of the
pedicle screw is applied by a user to rod 108.
[0045] Although fastener 402 is shown as having external threads
480, fastener 402 may instead be a non-threaded locking cap similar
or identical to that described in U.S. Provisional Patent
Application No. 60/674,877, filed Apr. 25, 2005, which is
incorporated herein by reference in its entirety. Saddle 414 may
also be attached to fastener 402 as part of an assembly.
Alternatively, fastener 402 may be of other types, and anchor head
404 may have corresponding features required to permit attachment
and operation of fastener 402.
[0046] Note that collet 410 may be advantageously used with other
headless anchor members and that the assembly of collet 410 and
headless pedicle screw 406 may be advantageously used with other
types of anchor heads, internal sleeves, and fasteners than those
shown herein. For example, collet 410 and screw 406 may be used
with the bone anchor disclosed in the previously cited U.S.
Provisional Patent Application No. 60/674,877, filed Apr. 25, 2005,
incorporated herein by reference in its entirety.
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